Short leg brace

ABSTRACT

A short leg brace which is composed of a foot mount and a calf splint pivotably attached to each other so as to allow plantar and dorsal flexions and which is provided with a compression spring between the splint and the heel portion of the mount for elastically hindering the plantar flexion.

TECHNICAL FIELD

The present invention relates to a short leg brace which is used bypatients who need support to their ankle joint when they walk.

BACKGROUND OF THE INVENTION

A short leg brace such as shown in FIG. 5 is conventionally known as asupport used by patients who, due to paralysis resulting from cerebralhemorrhage or cerebral thrombosis or due to hemiplegia resulting from anaccident, cannot move their ankle joint as they intend.

This conventional short leg brace is made of relatively rigid syntheticresin material, and comprises a foot mount 10A for supporting the footsole S and a calf splint 20A which is to be set along the calf C,wherein the foot mount 10A and the calf splint 20A are moldedintegrally. With the foot mount 10A placed under the foot and the calfsplint 20A set along the calf C, the short leg brace is secured by meansof fixing bands 50. Thus, the short leg braces of this type stabilizethe leg and the foot sole in an approximately right angle (so that theankle joint is set at its neutral position), and prevent both plantarflexion (the flexion in the direction that the toe drops down) anddorsal flexion (the flexion in the direction that the toe is lifted up)of the ankle joint so that talipes equinus and/or drop foot arecorrected.

Therefore, the short leg braces of this type fix the ankle jointrelatively firmly, preventing almost any motion of the ankle joint, andthus have a drawback that they cannot allow a patient to walk in anatural and smooth manner.

It might be possible to adjust the above shown conventional short legbrace by selecting the material thereof or by adjusting the width of thejunction 51 between the foot mount 10A and the calf splint 20A so as toprovide some flexibility to the short leg brace, and therefore it mightbe possible to change the width of the junction 51 depending on thecondition of the patient or on how far the patient's rehabilitationprogram has proceeded (by scraping the junction 51 so that its widthprogressively reduces as the rehabilitation program proceeds). However,because it is very difficult to restore the short leg brace if it isreduced excessively, such adjustment is seldom practiced but instead itis common to make the short leg brace anew every several years (underthe current Japanese Disabled Persons Welfare Act, it is permitted toremake the short leg brace every three years).

With the ankle joint fixed by a support, it is impossible for a patientto walk in a natural manner. FIG. 6 shows one cycle of walking. Thewalking cycle can be divided into a stance phase in which a leg ofinterest (the right leg in FIG. 6) is in contact with the floor and aswing phase in which the leg of interest is apart from the floor. In thedrawing, the stance phase is defined as a period between the heelcontact (a) and the toe separation (1), while the swing phase is definedas a period between the toe separation (1) and the next heel contact(p).

In this walking cycle, among the ankle joint dorsal flexion muscle(precisely the tibialis anterior, hereinafter referred to as the dorsalflexion muscle) and the ankle joint plantar flexion muscle (preciselythe triceps muscle of the calf, hereinafter referred to as the plantarflexion muscle), the one which is shown with a shade in FIG. 6 is theworking muscle. In the period from the heel contact (a) to the foot flat(b) at which the whole foot sole comes into contact with the floor, thedorsal flexion muscle works to prevent abrupt drop of the toe. In theperiod from the foot flat (b) through the heel separation (h) to the toeseparation (1), the plantar flexion muscle works to support the weight,move the center of gravity forward, and cause the toe to kick the floor.In the swing phase between the toe separation (1) and the next heelcontact (p), the dorsal flexion muscle works to lift up the toe so thata clearance is maintained between the foot and the floor. Thus, in thewalking action, the plantar and dorsal flexion muscles work alternatelyso that the ankle repeats the plantar and dorsal flexions.

Referring to FIG. 7, the period between the heel contact (a) and thefoot flat (b) is described in more detail in the following. In thisdrawing, K designates the knee (or the knee joint), W the center ofgravity, A the ankle (or the ankle joint), F the foot (or the part lowerthan the ankle), TH the thigh, and SH the shank. First, the foot F ismoved forward and the heel thereof is brought into contact with thefloor (this state is shown in the left-side drawings, and designatedwith HC which is an abbreviation of “heel contact”). Subsequently, asthe body moves forward (i.e., the center of gravity moves forward), thefoot is, via the state shown in the middle drawings, gradually broughtinto full contact with the ground until the toe contacts the floor (thisstate is designated with EF which is an abbreviation of “foot flat”).

In the period from HC to FF, a person without a disability can controlthe plantar flexion of his or her ankle joint as the weight is graduallyapplied to the foot from the left-side state to the right-side stateshown in FIG. 7(A). In other words, the dorsal flexion muscle graduallyexpands while preventing abrupt drop of the foot toe. As a result, theknee is substantially maintained on the line of action of.the vectorrepresenting the reaction force from the floor (the vector represents aresultant of the forces provided from the floor over the whole foot solewhen the weight is applied to the foot), which is shown in the drawingby the arrow directed upward from the floor, so that the person can walksmoothly and steadily.

However, the dorsal flexion muscle of a person with hemiplegia may beweakened and the plantar flexion muscle may have an extraordinarytension, always pulling the foot toe in the direction of plantarflexion. As a result, the foot toe comes into contact with the floorimmediately after HC, with the knee K positioned on a rear side withrespect to the line of action of the vector representing the reactionforce from the floor as shown in FIG. 7(B), leading to an overextensionof the knee K. To prevent this, the short leg brace is required to havean ability to assist the dorsal flexion muscle while at the same timeallowing the plantar flexion during the period from HC to FF.

In the case where the conventional short leg brace of FIG. 5 is used,because the short leg brace fixes the ankle joint in the neutralposition, it is necessary to move the whole lower leg forward in orderto accomplish the transition from HC to FF, as shown in FIG. 7(C). Thiscauses the knee K to be positioned excessively on the front side of theline of action of the vector representing the reaction force from thefloor, creating a problem that the knee K cannot be steadily controlledif the extensor muscle thereof is weak.

After FF in FIG. 7, the portion of the weight applied to the foot isgradually increased, causing the ankle joint A to bend in the directionof dorsal flexion, as shown by the step (c) and its subsequent steps inFIG. 6. In this period, the short leg brace is required to move freely(without a resist) in the direction of dorsal flexion so as not tohinder the natural motion of the ankle joint A. Thus, the short legbrace is required to assist the dorsal flexion muscle in the period fromHC to FF ((a)-(b)) and in the swing phase ((l)-(o)) in FIG. 6. Therequired supplementary torque during the swing phase is very small,because during this period the short leg brace only has to lift up thefoot. However, in the period from HC to FF, the required supplementarytorque is relatively large because the short leg brace has to preventabrupt drop of the foot toe against the weight increasingly applied tothe foot. Thus, if the short leg brace can produce an adequatesupplementary torque in this period, it will improve the user's walkover the whole walking cycle including the period after FF.

Examples of the prior art are disclosed in the specifications ofJapanese Patent Publication No.61-16173 and Japanese Utility ModelPublication No.61-43473.

The embodiment of No.61-16173 comprises a supporting member whichextends from the foot sole to an upper part of the Achilles tendon viaan outer side of the ankle. The supporting member can be secured to theleg by straps. Further, a calf splint is hinged to an upper end portionof the supporting member, and tension springs are used to urge the toeside portion toward the hinge between the supporting member and the calfsplint.

However, this conventional embodiment essentially fixes the ankle jointby means of the supporting member, and the resultant essentially limitedmovement of the ankle joint is elastically hindered by the tensionsprings. Therefore, the degree of assistance to the dorsal flexionmuscle and the allowable range of the plantar flexion are both quitelimited and insufficient to achieve natural movement of the ankle joint.

The embodiment of No.61-43473 is provided with a large flexibility (inother words, cat be bent with a small force) as a result of greatlyreducing the width of the joint 51 of the embodiment shown in FIG. 5,while a side strut having an S-shape so as to function as a spring isprovided in a manner that it extends upright with its upper endvertically slideably engaged to the calf splint 20 a.

In this way, with proper provision of a stopper for limiting thevertical sliding movement of the side strut, it is possible to generatea large resisting force against the plantar flexion while allowingsubstantially free dorsal flexion, so that an advantageous short legbrace is achieved. However, as the side strut is stretched orcompressed, its degree of flexion changes and the side strut can engageand irritate the skin of the leg, creating a problem that thisembodiment is not suitable for a long hour walking.

In view of such problems of the prior art, a primary object of thepresent invention is to provide a short leg brace which can assist thepatient in achieving more natural walking. It is also contemplated thatthe present invention can be used in an adaptability test conducted tofind a suitable supplementary torque for each patient with hemiplegia,in which the patient's walking condition is examined for variousmagnitudes of supplementary torque.

DISCLOSURE OF THE INVENTION

To achieve the above objects, the present invention provides a short legbrace comprising: a foot mount 10 for supporting a foot sole S; and acalf splint 20 to be set along a calf C, the foot mount 10 and the calfsplint 20 being pivotably attached to each other by a pivot 40 at anankle portion A so as to allow plantar and dorsal flexions; wherein acompression spring 31 is provided between the calf splint 20 and a heelportion H of the foot mount 10 so as to elastically hinder the plantarflexion of the foot mount 10.

Thus the compression spring 31 elastically hinders the plantar flexionof the foot mount 10 around the pivot 40, in other words, thecompression spring 31 functions to assist the ankle joint dorsal flexionmuscle during the period from HC to FF.

According to another aspect of the present invention, a short leg braceis provided which comprises: a foot mount 10 for supporting a foot soleS; and a calf splint 20 to be set along a calf C, the foot mount 10 andthe calf splint 20 being pivotably attached to each other by a pivot 40at an ankle portion A so as to allow plantar and dorsal flexions;wherein a compression spring 31 is provided between the calf splint 20and a heel portion H of the foot mount 10 so as to elastically hinderthe plantar flexion of the foot mount 10 with a torque greater than orequal to 5 Nm and less than or equal to 20 Nm for 10 degree plantarflexion angle of the foot mount 10.

A suitable magnitude of the supplementary torque is determined dependingon various factors such as the degree of disability, muscle strength,age, sex, weight, etc. of each patient. Besides, the suitable magnitudeof the supplementary torque may change as the rehabilitation programproceeds. Numerous actual tests of the short leg brace have shown thatit is preferable that the supplementary torque for the 10 degree plantarflexion angle of the ankle joint is adjustable within a range from 5 to20 Nm. Thus, by using the compression spring 31 which is capable ofelastically hindering the plantar flexion with a torque of 5-20 Nm forthe 10 degree plantar flexion angle, it is possible to achieve a shortleg brace which is simple and compact, but is capable of providing anadequate supplementary torque.

According to yet another aspect of the present invention, a short legbrace is provided which comprises: a foot mount 10 for supporting a footsole S; and a calf splint 20 to be set along a calf C, the foot mount 10and the calf splint 20 being pivotably attached to each other by a pivot40 at an ankle portion A so as to allow plantar and dorsal flexions;wherein the short leg brace further comprises: a spring housing 30 whichhas an upper end connected to the calf splint 20 and in which areaccommodated a compression spring 31 and a slider 32, the slider 32having a lower portion projecting out through a lower end of the springhousing 30 and being moveable within the spring housing 30 so as to becapable of compressing the compression spring 31; and a telescopic shaft33 which is passed through the slider 32 so as to be slideable in theslider 32 and which has in its lower portion a stopper part 33 a adaptedto abut an outer surface of the slider 32, with a lower end of thetelescopic shaft 33 connected to a rear side of a heel portion H of thefoot mount 10.

In this way, when the foot mount 10 is moved in the direction of plantarflexion, the telescopic shaft 33 is pushed deeper into the springhousing 30, and after the stopper part 33 a abuts the slider 32, thecompression spring 31 is compressed to generate a force for assistingthe ankle joint dorsal flexion muscle. On the other hand, when the footmount 10 is moved in the direction of dorsal flexion, the telescopicshaft 33 freely travels without engaging the compression spring 31 andtherefore without hindering the dorsal flexion. Since the slidingmovement of the telescopic shaft 33 is guided by an inner surface of theslider 32 which can be formed in a relatively elongate shape, highstructural strength is achieved. In stead of the combination of thetelescopic shaft and the slider as shown above, it may be possible tointegrally form the telescopic shaft and the slider, use one orplurality of springs having a non-linear compression profile in that thereaction force generated by the springs abruptly increases from acertain point, and set the slider in the spring housing 30 so that inthe neutral position the slider slightly pushes the springs. In this wayalso, similar effects to those of the above embodiment can be obtained,or it may be possible to allow the ankle joint to move freely in thedirection of dorsal flexion while elastically hindering the plantarflexion beyond a prescribed angle, except that some elastic force isapplied to the ankle joint in its neutral position.

According to yet another aspect of the present invention, a short legbrace is provided which comprises: a foot mount 10 for supporting a footsole S; and a calf splint 20 to be set along a calf C, the foot mount 10and the calf splint 20 being pivotably attached to each other with apivot 40 at an ankle portion A so as to allow plantar and dorsalflexions; wherein the short leg brace further comprises: an upperbracket 34 secured to the calf splint 20; an attachment piece 34 bpivotably connected to the upper bracket 34 around a horizontal axis 34a extending in a lateral direction with respect to the foot; a threadedrod member 35 engaged to a lower end of the attachment piece 34 b insuch a manner that its position relative to the attachment piece 34 b isadjustable; a spring housing 30 engaged by the threaded rod member 35,the spring housing containing therein a compression spring 31 and aslider 32, the slider 32 having a lower portion projecting out through alower end of the spring housing 30 and being moveable within the springhousing 30 so as to be capable of compressing the compression spring 31;a telescopic shaft 33 which is passed through the slider 32 so as to beslideable in the slider 32 and is provided in its lower portion with astopper part 33 a adapted to abut an outer surface of the slider 32; anda lower bracket 36 which is pivotably connected to a lower end of thetelescopic shaft 33 around a horizontal axis 36 a extending in a lateraldirection with respect to the foot and which is secured to a rear sideof a heel portion H of the foot mount 10.

In this way, by changing the position of the threaded rod member 35relative to the attachment piece 34 b, it is possible to adjust thepoint where the compression spring begins to be compressed as a resultof the plantar flexion. Specifically, when the threaded rod member 35has been screwed deep into the attachment piece 34 b, a large plantarflexion angle of the ankle joint is required to begin to compress thecompression spring 31, while when the threaded rod member 35 has beenscrewed less deep into the attachment piece 34 b so that the distancebetween the spring housing 30 and the attachment piece 34 b has becomerelatively large, the compression spring 31 begins to be compressed witha relatively small plantar flexion angle.

Thus, the short leg brace according to the present invention can enablea patient to walk smoothly by assisting the dorsal flexion muscle withthe compression spring 31 while allowing the plantar and dorsal flexionsof the ankle joint.

Since the compression spring 31 is easily replaceable, the torque Aprovided from the short leg brace to assist the dorsal flexion can beadjusted so that it suits to a condition of each patient.

By setting the supplementary torque from the compression spring 31within a range from 5 Nm to 20 Nm, it is possible to achieve such anassistance to the dorsal flexion muscle as was not contemplated in theprior art.

By utilizing the spring housing 30, compression spring 31, slider 32 andtelescopic shaft 33, with the upper end of the spring housing 30connected to the calf splint 20 and the lower end of the telescopicshaft 33 connected to the foot mount 10, a short leg brace is providedin which the movement of the foot mount 10 in the direction of dorsalflexion is not hindered by the compression spring 31.

The structure in which the threaded rod member 35 is engaged to thelower end of the attachment piece 34 b in such a manner that itsposition relative to the attachment piece 34 b is adjustable and thespring housing 30 meshes with the threaded rod member 35 allowsadjustment of the ankle joint angle at which the compression spring 31begins to be compressed, and accordingly the ankle joint angle at whichthe supplementary torque begins to be generated can be suitably set foreach patient.

Other features. and objects of the present invention will be apparentfrom the following description taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a frontal view showing one embodiment of the presentinvention.

FIG. 2 is a longitudinal cross sectional view of a spring housing usedin another embodiment.

FIG. 3 is a side view of the spring housing.

FIG. 4 is a partial longitudinal cross sectional view of a yet anotherembodiment of a spring housing.

FIG. 5 is a frontal view of a conventional embodiment.

FIG. 6 is a schematic diagram for explaining a walling cycle.

FIG. 7 is a schematic diagram for explaining a part of the waling cycle.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, embodiments of the present invention are describedwith reference to the accompanied drawings. The numeral reference 10denotes a foot mount, and the numeral reference 20 denotes a calfsplint. The foot mount 10 is made of a relatively rigid synthetic resinmaterial and supports the foot sole S (as well as the heel H). The footmount 10 comprises a flat portion somewhat larger than the foot sole anda pair of upright side walls 11, 11 so that the foot mount 10 cannot bedeformed easily.

The calf splint 20 is also made of a relatively rigid synthetic resinmaterial and has a generally trough-like shape adapted for being setalong the calf C. As in the conventional embodiment, the calf splint 20and the foot mount 10 can be secured to the leg with fixing bands 50, 50or the like.

The foot mount 10 and the calf splint 20 are pivotably attached to eachother by pivots 40 at an ankle portion A so as to allow plantar anddorsal flexions. Although not shown in the drawings, the pivots 40 areprovided on opposite lateral sides of the foot so that they do notengage the somewhat protruding ankle portion A of the patient when theshort leg brace is fitted to the patient.

The short leg brace further comprises a compression spring 31 disposedbetween the calf splint 20 and the foot mount 10 in order to elasticallyhinder the plantar flexion of the foot mount 10.

The compression spring 31 for elastically hindering the plantar flexionworks to assist the dorsal flexion muscle. To the calf splint 20 ispivoted an upper end of a spring housing 30 elongating in a generallyvertical direction as shown in FIG. 1, and the compression spring 31 isaccommodated in an upper part of the spring housing 30. Under thecompression spring 31 in the spring housing 30 is accommodated a slider32 such that the slider 32 can slide inside the spring housing 30 tocompress the compression spring 31. The lower portion of the slider 32projects out of the spring housing 30. Further, a shaft 33 whose lowerend is pivotably connected to the heel portion of the foot mount 10extends through the slider 32. The shaft 33 has a stopper part 33 aadapted to abut the lower end of the slider 32. In this way, when thefoot mount 10 moves in the direction of plantar flexion and the shaft 33travels upward, the stopper part 33 a pushes the slider 32 upward, whichin turn compresses the compression spring 31. On the other hand, whenthe foot mount 10 moves in the direction of dorsal flexion from thestate shown in FIG. 1, the shaft 33 freely travels downwardly withoutany interaction with the compression spring 31. To prevent thecompression spring 31 from pushing out the slider 32 from the springhousing 30, the outer diameter of the portion of the slider 32 containedinside the spring housing 30 is larger than that of the opening formedin the lower end of the spring housing 30.

Thus, when the foot mount 10 rotates around the pivot axis 40 in thedirection of plantar flexion with its toe side portion moving downwardlyfrom the state shown in FIG. 1, the shaft 33 is caused to move upwardlytogether with its stopper part 33 a and pushes the slider 32 so as tocompress the compression spring 31. The force (not shown in the drawing)generated by the compression spring 31 when the spring 31 is compressedas a result of the plantar flexion of the ankle joint fitted with theshort leg brace of the present invention works as a resisting forceagainst the plantar flexion, in other words, the compression spring 31provides a force urging the heel portion H of the foot mount 10 in thedownward direction or provides a supplementary torque to the dorsalflexion muscle.

Conventionally, because it was customary to fix the ankle joint in amanner such as shown in FIG. 5, the magnitude of supplementary torquerequired for assisting the dorsal flexion muscle had not been studiedsufficiently, and no concrete values thereof had been obtained. Thus,numerous actual tests of the short leg brace were conducted to show thata supplementary torque of 5-20 Nm was necessary for the foot mount 10'splantar flexion angle of 10 degrees. Therefore, in order to achieve sucha supplementary torque for assisting the dorsal flexion muscle, it ispreferred to use a compression spring which can elastically hinder the10 degree plantar flexion of the foot mount 10 with a torque greaterthan or equal to 5 Nm and less than or equal to 20 Nm as the abovecompression spring 31.

If one end of the compression spring 31 were connected to the foot mount10 and the other end thereof to the calf splint 20, the compressionspring 31 would also function as a tension spring. However, as mentionedabove, in the walking cycle the ankle joint needs to move in thedirection of dorsal flexion preferably without any resisting forcegenerated from the spring. In order to prevent the spring from hinderingthe dorsal flexion, in the embodiments shown in FIGS. 1 and 2, thespring housing 30 has an upper end connected to the calf splint 20; thecompression spring 31 and the slider 32 are accommodated in the springhousing 30, the slider 32 having a lower portion projecting out througha lower end of the spring housing 30 and being moveable within thespring housing 30 so as to be capable of compressing the compressionspring 31; and a telescopic shaft 33 having in its lower portion astopper part 33a adapted to abut an outer surface of the slider 32 ispassed through the slider 32 so as to be slideable in the slider 32,with a lower end of the telescopic shaft 33 connected to a rear side ofa heel portion of the foot mount 10.

Thus, if the telescopic shaft 33 in the state shown in FIG. 2 isprovided with a force urging it deeper into the spring housing 30 (aforce which is directed upwardly with respect to the drawing and whichis caused as a result of the plantar flexion), the compression spring 31is compressed. On the other hand, if a force urging the telescopic shaft33 toward outside the spring housing 30 (a force which is directeddownwardly with respect to the drawing and which is caused as a resultof the dorsal flexion) is applied to the telescopic shaft 33 in thestate shown in FIG. 2, the telescopic shaft merely travels outwardwithout interaction with the compression spring 31.

In order to prevent the telescopic shaft 33 from dropping off from thespring housing 30, a stopper 33 b is formed such that when the shaft 33is withdrawn from the housing 30 to a predetermined extent, the stopper33 b abuts an upper end of the slider 32 to prevent further withdrawalof the shaft 33. The stopper 33 b is formed in a shape of an arrowheadhaving a longitudinal slit so that the telescopic shaft 33 can beinserted through a central longitudinal bore of the slider 32 but onceinserted cannot be removed with an ordinary force.

As describe above, the supplementary torque for assisting the dorsalflexion muscle was measured in numerous actual tests as being in therange of 5-20 Nm, and therefore it is preferred that the toque isadjustable within such a range.

Thus, a short leg brace is provided which comprises: an upper bracket 34secured to the calf splint 20; an attachment piece 34 b pivotablyconnected to the upper bracket 34 around a horizontal axis 34 aextending in a lateral direction with respect to the foot; a threadedrod member 35 engaged to a lower end of the attachment piece 34 b insuch a manner that its position relative to the attachment piece 34 b isadjustable; a spring housing 30 engaged by the threaded rod member 35 sothat the rod member 35 can be screwed into and out of the spring housing30 by turning the rod member 35 relative to the spring housing 30, thespring housing containing therein a compression spring 31 and a slider32, the slider 32 having a lower portion projecting out through a lowerend of the spring housing 30 and being moveable within the springhousing 30 so as to be capable of compressing the compression spring 31;a telescopic shaft 33 which is passed through the slider 32 so as to beslideable in the slider 32 and is provided in its lower portion with astopper part 33 a adapted to abut an outer surface of the slider 32; anda lower bracket 36 which is pivotably connected to a lower end of thetelescopic shaft 33 around a horizontal axis 36 a extending in a lateraldirection with respect to the foot and which is secured to a rear sideof a heel portion H of the foot mount 10.

The upper bracket 34 is secured to the calf splint 20, while the lowerbracket 36 is secured to the foot mount 10. The horizontal axes 34 a and36 a are provided so that the plantar and dorsal flexions are notprevented by connecting the calf splint 20 and the foot mount 10 to eachother at positions other than the pivot 40.

The structure in that the threaded rod member 35 is engaged to the lowerend of the attachment piece 34 b in such a manner that its positionrelative to the attachment piece 34 b is adjustable makes it possible tochange the position of the spring housing 30, and thereby adjust theposition at which the compression spring 31 begins to be compressed bythe plantar flexion. Specifically, if the threaded rod member 35 issecured at a higher position than that shown in FIG. 2, the position atwhich the upwardly traveling telescopic shaft 33 begins to compress thecompression spring 31 also becomes higher. Thus, by changing theposition of the spring housing 30 it is possible to adjust the angle ofthe ankle joint at which the supplementary torque begins to be exerted.

As shown in FIG. 4, a spacer 39 can be fitted on a part of thetelescopic shaft 33 between the stopper 33 a and the slider 32. Thespacer 39 can consist of for example a C-ring having a proper thickness.By suitably selecting the thickness, the angle of the ankle joint atwhich the supplementary torque begins to be exerted can be adjusted in asimilar manner to that described above.

In the embodiment shown in the drawing, the spring housing 30 is engagedby the threaded rod member 35 so that the rod member 35 can be screwedinto and out of the spring housing by turning the rod member 35 relativeto the spring housing 30. This also allows adjustment of the compressionforce of the compression spring 31. If the threaded rod member 35 ispositioned so that a longer part thereof protrudes over the springhousing 30 than the state shown in FIG. 2, the compression spring isbrought into a pre-compressed state with a somewhat reduced total lengththereof, requiring a larger force for its further compression, in otherwords, resulting in a larger supplementary force for assisting thedorsal flexion muscle.

Although the spring force generated by the compression spring 31 isadjustable, it may be difficult in practice to adjust the spring forcewithin the above mentioned range of 5-20 Nm. In such a case, a pluralityof compression springs 31 which have different characteristics and whichcan be replaceable with each other may facilitate achieving a suitablesupplementary torque for assisting the dorsal flexion muscle.

In the drawing, the reference numerals 37, 37 denote securing nuts,while the reference numeral 38 denotes a component part for receivingthe threaded rod member.

Although the present invention has been described as a short leg brace,the present invention can be used in determining an optimum magnitude ofsupplementary torque for each patient. In such a case, the short legbrace is temporarily fitted on the patient and then the patient'swalking condition is examined. By using the test results, a short legbrace whether according to the present invention or of the prior art canbe manufactured more efficiently.

Although the present invention has been described in terms of preferredembodiments thereof, it is obvious to a person skilled in the art thatvarious alterations and modifications are possible without departingfrom the scope of the present invention. For example, instead of thecompression spring, any elastic member such as a torsion spring or atension spring can be used to embody the present invention.

What we claimed is:
 1. A short leg brace, comprising: a foot mount (10)for supporting a foot sole (S); and a calf splint (20) to be set along acalf (C), the foot mount (10) and the calf splint (20) being pivotablyattached to each other by a pivot (40) at an ankle portion (A) so as toallow plantar and dosal flexions; wherein an elastic member assembly isprovided between the calf splint (20) and a heel portion (H) of the footmount (10), elastic member assembly comprising: a first portion havingat its one end a pivot part which is pivotably connected to one of thecalf splint (20) or a heel portion (H) of the foot mount (10); a secondportion having at its one end a pivot part which is pivotably connectedto the other one of the calf splint (20) or the heel portion (H) of thefoot mount (10); and a compression spring (31) disposed between thefirst and second portion; the first portion and the second portion beingengaged so that they can move toward and away from each other; wherebythe elastic member assembly applies such an elastic force to the footmount (10) as to urge the same in a direction of the dorsal flexionthereof when an ankle joint is on a plater flexion side with respect toa prescribed ankle joint angle while applying substantially no elasticforce to the foot mount (10) when the ankle joint is on a dorsal flexionside with respect to the prescribed ankle joint angle during use.
 2. Ashort leg brace according to claim 1, wherein the first portioncompression a spring housing (30) for accommodating the compressionspring (31); and the second portion comprises: a slider (32) slideablydisposed in the spring housing (30) so as to compress the compressionspring (31), the slider (32) having stopper means for preventing theslider (32) from being released from the spring housing (30) and a boreextending in a direction of the sliding movement; and a telescopic shaft(33) slideably received in the bore of the slider (32) and having oneend connected to the pivot part of the second portion; wherein theslider (32) and the telescopic shaft (33) have respective stoppersurfaces which are adapted to abut each other and limit a motion of thetelescopic shaft (33) toward inside of the bore of the slider (32) so asto define the prescribed ankle joint angle.
 3. A short leg braceaccording to claim 2, further comprising means (39) for adjusting adistance between the stopper surface of the telescopic shaft (33) andthe pivot part of the second portion.
 4. A short leg brace according toclaim 2, further comprising means for adjusting a distance between thestopper surface of the slider (32) and the pivot part of the firstportion in a state that the stopper surface of the slider (32) and thestopper surface of the telescopic shaft (33) do not abut each other. 5.A short leg brace according to claim 1, further comprising means foradjusting the prescribed ankle joint angle.
 6. A short leg braceaccording to claim 1, wherein the elastic member assembly elasticallyhinders the plantar flexion of the foot mount (10) with a torque greaterthan or equal to 5 Nm and less than or equal to 20 Nm for 10 degreeplantar flexion angle of the foot mount (10).
 7. A short leg brace,comprising: a foot mount (10) for supporting a foot sole (S); and a calfsplint (20) to be set along a calf (C), the foot mount (10) and the calfsplint (20) being pivotably attached to each other by a pivot (40) at anankle portion (A) so as to allow plantar and dorsal flexions; whereinthe short leg brace further comprises: an upper bracket (34) secured tothe calf splint (20); an attachment piece (34 b) pivotably connected tothe upper bracket (34) around a horizontal axis (34 a) extending in alateral direction with respect to the foot; a threaded rod member (35)engaged to a lower end of the attachment piece (34 b) in such a mannerthat its position relative to the attachment piece (34 b) is adjustable;a spring housing (30) engaged by the threaded rod member (35), thespring housing containing therein a compression spring (31) and a slider(32), the slider (32) having a lower portion projecting out through alower end of the spring housing (30) and being moveable within thespring housing (30) so as to be capable of compressing the compressionspring (31); a telescopic shaft (33) which is passed through the slider(32) so as to be slideable in the slider (32) and is provided in itslower portion with a stopper part (33 a) adapted to abut an outersurface of the slider (32); and a lower bracket (36) which is pivotablyconnected to a lower end of the telescopic shaft (33) around ahorizontal axis (36 a) extending in a lateral direction with respect tothe foot and which is secured to a rear side of a heel portion (H) ofthe foot mount (10).